Cardiac deformation indices such as strain, strain rate, and time to maximal strain are valuable in early detection of heart disease and hold tremendous prognostic value in assessing patients recovering from heart failure. These indices have been previously measured in modalities such as Doppler echocardiography and magnetic resonance imaging. However, cardiac deformation has not been well characterized in X-ray computed tomography (CT), a modality whose balance of high acquisition speed and good temporal and spatial resolution makes it highly desirable in the clinical setting. The current work, an extension of our group's previously published cardiac motion estimation algorithm, calculates deformation indices such as strain, strain rate, maximum strain, and time to maximal strain from four-dimensional motion vector field data. Along each dimension, calculations are made between every adjacent pair of grid points, thus striving for simplicity while yielding an increase in spatial resolution over approaches that divide the heart into a number of segments. Results are visualized as semi-transparent color maps superimposed on CT image slices in the short-axis view and the two long-axis views. Results agree with the expected behavior of myocardial contraction. Animal studies are underway to better assess the physiologic accuracy of the calculated deformation indices as well as to compare the results with those from other imaging modalities. The present work and its further refinements may yield rich yet easily accessible information for clinicians in early diagnosis and follow-up monitoring.